In recent years, non-conventional fossil resources such as shale gas and shale oil have been actively recovered. The recovery of shale gas and shale oil is carried out through three steps: vertical drilling, horizontal drilling, and hydraulic fracturing. The hydraulic fracturing is a technique in which fractures are created in formations in a well by water pressure to form highly permeable channels, and as treating liquids in this technique, various materials are used according to the function. The materials added are desirably environmentally friendly materials, and biodegradable plastics have also been used.
Poly(lactic acid) is a practically melt-moldable polymer having a melting point of around 170° C., and because of having biodegradable characteristics, it has been developed as a biodegradable plastic that will be degraded after use in the natural environment to be emitted as carbon dioxide gas and water. In addition, poly(lactic acid) itself is made of a renewable resource (biomass) originated from carbon dioxide and water, and, therefore, carbon dioxide, if emitted after use, has no effect on the amount of carbon dioxide in the global environment. Such a carbon-neutral nature has received attention in recent years, and poly(lactic acid) is expected to be used as an eco-friendly material. Furthermore, since lactic acid, a monomer of poly(lactic acid), has been produced at low cost by fermentation methods using microorganisms, poly(lactic acid) is being studied as a material alternative to general-purpose polymers made of petroleum-based plastics.